(a) Technical Field
The present invention relates to a method and a process of preparing precipitated calcium carbonate of high purity by extracting calcium ion contained in an alkali ion-containing inorganic material such as mineral, steelmaking slag and waste concrete with the use of an acidic aqueous solution, separating other metal ions from the extracted solution, preparing an alkaline earth metal hydroxide using an alkaline aqueous solution and then contacting the same with carbon dioxide.
(b) Background Art
The technology of preparing calcium carbonate from alkali ion-containing inorganic materials using carbon dioxide through an inorganic carbonation reaction has been consistently studied since its importance was reported by Seifritz (Nature, 345, 486 (1990)).
In the early years, a method of fixing carbon dioxide by injecting carbon dioxide directly into mineral was devised as in W. J. J. Huijgen and R. N. J. Comans, ERC report, ECN-C-05-022 (2005). However, the reaction rate was too slow and the cost of pretreatment was too high.
Later, a method of extracting calcium using acetic acid and then carbonating the same was developed by R. Zevenhoven, S. Eloneva, and S. Teir (Catal. Today, 115. 73 (2006)). However, the method lacked economical efficiency because the recovery of acetic acid was difficult.
Also, a method of using an acid and an alkali to extract alkali ions from mineral was devised by S. Teir, R. Kuusik, C.-J. Fogelhom and R. Zevenhove (Int. J. of Miner. Proc., 85, 1 (2007)). However, there was a problem that the acid used as an extractant and the alkali used as a precipitator are expensive so that the preparation cost was too high.
Korean Patent Registration No. 10-1157909 developed a method of preparing a carbonate from steelmaking slag. This method separates slag from reactants by providing boron oxide to a reaction solution and then prepares calcium carbonate by injecting carbon dioxide. However, this method is problematic in that the yield and quality of calcium carbonate are low.
Korean Patent Publication No. 10-2012-0059254 developed a method of extracting calcium ions from natural mineral or steelmaking slag using an acid such as acetic acid, etc. and preparing calcium carbonate at a relatively low pH. However, this method is problematic in that the production cost of calcium carbonate is high with regard to recovery of the acid.
Various researches have been made to solve these problems and reduce the production cost of calcium carbonate.
U.S. Pat. No. 7,790,012 B2 developed a method of preparing sodium hydroxide by oxidizing hydrogen produced from a chloralkali process at a low voltage and then preparing calcium carbonate for a cement by desalinating calcium ions contained in brine or seawater using the same.
And, Korean Patent Publication No. 10-2015-0080687, developed by the inventors of the present invention, provided a method of preparing sodium hydroxide and hydrochloric acid through electrolysis of sodium chloride, extracting calcium ions from an inorganic material using the hydrochloric acid and then preparing sodium bicarbonate or sodium carbonate by providing carbon dioxide to the sodium hydroxide, thereby preparing calcium carbonate from calcium ions.
The production cost of calcium carbonate could be reduced by the above methods. However, the calcium carbonate prepared through the methods has low purity because impurities such as aluminum, magnesium, iron, etc. are included. In addition, the calcium carbonate has been used at low costs only for making cement due to its large particles. Although the calcium carbonate is prepared from high priced acids and alkali it is used only as a low-priced raw material for cement so that the calcium carbonate is proved uneconomical.